Ion gauge



s. BASHKIN April 10, 1951 ION GAUGE Filed Feb. '7, 1949 Fi g.l.

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INVENTOR. STANLEY BASHKIN /mM/flw Patented Apr. 10, 19 51 c UNITEDSTATES PATENT OFFICE ION GAUGE Stanley Bashkin, Madison, Wis., assignorto the United States of America as represented by the United StatesAtomic Energy Commission Application February 7, 1949, Serial No. 75,043

2 Claims. (01. 313-293) I The present invention relates to an improvedion gauge. Conventional ion gauges consist of an air-excluding jacketenclosing three concentrically arranged electrodes, the filament beingthe innermost electrode, the grid being a cylindrical electrodesurrounding the filament electrode and the ion collector electrode beinga cylindrical electrode surrounding the previous two. The filamentelectrode is electron emissive. It is surrounded by the positivelycharged grid electrode, and this in turn is surrounded by the ioncollector electrode which is negatively charged with respect to the gridelectrode and the filament electrode. from the electron emissivefilament electrode are accelerated by the positive charge on the gridelectrode and those which do not strike the grid electrode directly arecaused to oscillate around the strands of which it is composed, untilthey are captured by the grid electrode or ions are formed when theelectrons strike gas molecules. The ions formed by the rapidly movingelectrons are, for the most part, positively charged ions. One of thedifiiculties arising from the arrangement of electrodes in suchpreviously known ion gauges is the trapping of positively chargedions inthe volume defined within the grid electrode. Because of the relativelyhigh potential on the grid electrode the positive ions, formed in thevolume defined within said grid electrode, are repulsed from the gridelectrode and alarge number thereof are caused to strike the filamentelectrode to which they are attracted. This action results in twodeleterious efiects on the conventional ion gauge. One of these is thereduction in sensitivity which follows 'from the reduced In operation,electrons emitted number of positive ions reaching the ion collectorplate. The second is the reduced life of the filament electroderesulting from the bombardment thereof by the positively charged ionsenclosed within the volume defined by the grid electrode. The secondefiect is usually evidenced by the formation of a carbonaceous depositon the filament electrode or of the wearing through and breaking of saidelectrode either of which necessitates frequent replacement thereof.

It is accordingly an object of the present invention to provide an iongauge having a greater sensitivity than previously known ion gauges.

It is another object of the present invention to provide an ion gaugewhich retains its sensitivity over a longer period of time.

It is a further object of the present invention 7 to provide an iongauge which minimizes the bombardment of the filament and the formationthereon oi a carbonaceous deposit.

means adaptable to be connected with a vessel which may contain gas atvery low pressure, an electrode assembly including a grid electrode, anion collector electrode and a filament electrode within said ,means,said filament electrode being positioned-between at least a portion ofsaid grid. electrode and at least a portion of said collector electrodeso thatcharged particles passing from said filament to said portion ofsaid collector electrode do not pass through a grid electrode, and meansfor measuring the current flowing to said collector electrode. V

' Two embodiments of the present invention are illustrated in theaccompanying drawing and the manner of achievement of the objects of thepresent invention may be explained more clearly with reference to thedrawing wherein:

Figure 1 is an elevation of a tube assembly with the jacket broken awayalong broken line l| of Figure 2 and with a part of the collectorelectrode broken away.

Figure 2 is a horizontal section taken on the line 22 of Figure l.Figure 3 is' an elevation of another tube assembly with the jacketbroken away along broken line 3 -3 of. Figure 4 and with a part of itscollector electrode broken away. j

Figure 4 is a horizontal section taken on line 4-4 of Figure 3. g g j IReferring toFigures 1 and 2, gas is excluded from. an electrode assemblyby a glass jacket I00. The jacket is preferably made of glasses such asthose generally designated as Pyrex and Nonex. The jacket is essentiallyPyrex glass with Nonex glass sealed thereto atthe portions of the jacketI00 through which electrical contacts are sealed for connecting theelectrode assembly with the tube exterior. The seal through the Nonexportions 90, 92; 94- and 96 was made by means of 10 mil tungsten wiresH5, H1, I09 and ll'll. The chamber enclosed by the glass jacket I00 maybe connected to a system which may contain gas at a very low pressure bymeans of the tapered ground glass joint 88. As in conventional iongauges, electrons areemitted from a heated filament I06 which issupported on the nickel rods I 13 and Ill which are'in turn connectedrespecr 3 tively to the tungsten leads II! and H5, said leads beingsealed through the jacket I at the Nonex portions 90 and 92respectively. The emitted electrons bombard the gas present within thejacket Ito and cause ionization of said gas. An ionic current thereforeflows between the filament I00 and .a collector plate I02 which collectsthe ions formed by the electrodes. The current in tensity bears such arelation to the pressure or gas present in the jacket I00 that thepressure may be measured by measuring the current flowing to thecollector plate I02.- Electrical connection is made between the filamentI06 and the collector plate I02 through an external current measuringdevice (not shown The positioning of the collector plate I02 in thejacket I00 and the electrical connection to the jacket exterior iseffected by the nickel rod I05 and the tungsten tioned within the volumedefined by the generally cylindrically shaped collector plate I02 inrelatively closeproximity to the filament I06. Such a grid may be in theform of a conductive strand crimpd in a zigzag configuration to define agenerally rectangular shape.

\ As an example of the tube dimensions in one tube such as thatillustrated in Figure l, which tube was found to operate with higherefficiency than the conventional tubes, the following dimens'ion werefound satisfactory. were approximately 2 inches in height. wholeassembly was enclosed in a jacket of about 2 inches in diameter, thecollector being spaced about A; .of an inch. from the jacket wall. The

H4 by causing a suitable high voltage to be placed on a grid IIE whichis disposed between the filament I I8'and the outer collector plate II4. Such a grid may have, for example, a helical shape. Electricalconnection to the tube exterior from the grid I I6, the filament H0 andthe collector plate I20 and II 4 is made by means of the nickel rodsI30, I32 and I34 respectively and the tungsten leads I35, I38 and I40respectively, said leads being sealed through the Nonex portions I42,I44 and I40 of the jacket IIO. Conventional electrical supply andmeasuring apparatus (not shown) is employed in the external circuit.

The following is offered as an explanation of the more efiicientoperation of ion gauges pro- 'vided by the present invention over thoseprovided by prior ion gauges although it will be understood that theconcept of the present invention is not limited by the accuracy of thisexplanatioh. Referring to Figure 2; electrons are emitted from filamentI06. Those electrons which are emitted toward the portion of the ioncollect'or I92 on the filament side of broken line A'A will be repulsedby the low potential on the ion collector 102 toward the grid I04. Thehigh potential on the grid I04 'will attract the elec trons repulsedfrom the aforementioned portion ,7 of the ion collector 92 past thefilament I00 and The electrodes 7 The filament wasspace'dabout of aninch from the ja'jkt wan alld th grid, which had a Width 0f about of aninch. was spaced about of an inch from the same point on the jacket wallfrom which the filament was spaced of an inch. Electrical connection wasmade from the v grid I04 to an external voltage control means (notshown) through the nickel rod IOI and the tungsten l'ead I09 which wassealed through the jacket I00 at the Nonex portion 94 thereof. A benttungsten wire having a thickness of about 10 mil was found suitable forthe filament I06 and the grid I04 and a nickel foil of approximately 5mil in thickness, formed into a generally cylindrical shape, was foundsuitable asa collector plate "I02. All metal tometal connections weremade by spot welding. Conventional external electrical supply and'detectioh means were used in conjunction with the tube. Q 7

Many alternatives of the electrode arrangement whereby at least aportion of the filament electrode is disposed between at least a portionof the collector electrode and a portion of the, grid electrode suchthat electrons may pass between the portions of the filament andcollector electrodes without passing through a grid will be apparent toone familiar with the art. One such arrangement is illustrated inFigures 3 and 4 wherein gas is excluded from an electrode assembly by aglass jacket IIO which may be connected to a system which maycontain gasat very low pressure by means of the tapered ground glass joint 80.Electrons are emitted within said jacket IIO from a filament H8 andcause ions to form, which ions pass to either an inner collector plateI20 or an outer collector plate H4.

The electrons emitted from the filamentl I8 are accelerated outwardlytoward the collector pate some of those electrons which do not strikethe grid I0 4 "will oscillate around the strands thereof until they havestruck a molecule and formed an ion, or until they strike the grid I04.Some of the electrons emitted from filament I05 toward the grid side ofthe collector plate I02 will proceed directly toward the grid I04, andwill spiral around said grid I04 as hereinabove described. Whateverpositive ions are formed along'any of these electrons paths will be insuch a position with respect to the ion collector plate I02 that theywill not have to pass through the grid I04 to'rea'ch said collectorplate I 02 and thus substantially all positivejions formed will becollected on collector plate I02.

H A similar phenomenon occurs in the apparatus illustrated in Figures 3and 4; Positive ions ;-'-mee between the filament I I8 and the collectorlfiiil will be attracted to the collector I20 since the semesterpotential is below that of the filament potential. Similarly. ionsformed between the grid electrodel I6 and th'e'filame'nt electrode H8collected without any interference on the "outer collector I I4.

The materials and potentials which may be used in the present inventionare "substantially the sameas those used'i'n a conventional ion gauge.For example, the grid potential may be kept'a't about volts above thefilamentpotential and the" collector maybe kept at a potentialapproximately 20 volts below theiilament'p'otential. The substitution ofother materials for the nickel and tungsten employed in thedisclosedembodimnts is not 'a departure from the scope of the present"htion. It is desirable to keep the volume of the'i'on gauge relativelysmall, thus, for example, thespace between the collector electrode and,the envelope serves ho useful purpose and should be minimized.

1 foam to operate with higherefiiciency and with greater sensitivitythanpreviaany rmbwngauges.

The useful life of the filament is greatly extended and relatively smalldeposits of carbonaceous material form within comparable time to that inwhich filaments of previously known ion gauges were coated so as tomaterially reduce the efficiency of the gauge. In addition, the filamentof such a gauge was not Worn away after continued use to the extent thatcould be expected for previously used gauges.

It is apparent from the foregoing that the present invention provides avery highly efficient gauge. It will be understood that the scope of thepresent invention is not limited to the two illustrative embodiments setforth and represented in the figures but that other variations may beemployed without departing from the substance of the present concept.Thus, for example, filaments might be disposed on both sides of the gridI04 rather than on the one side only as indicated by the broken line I05in Figure 2. Similarly, a filament and grid and collector plate might beincorporated in that order outside the collector plate of either of theillustrative embodiments set forth thus making a series of collector,filament, grid, collector, filament, etc, Other variations which providefree access of ions formed in the ion gauge to the collector plate willbe apparent to those familiar with the art.

Since many embodiments might be made in the above-described inventionand since many changes might be made in the embodiment illustrativelydisclosed herein, it is to be understood that all matter hereinabove setforth is to be interpreted as illustrative only and not in a l m gsense,

comprises gas-excluding means adapted to be connected with a vesselwhich contains gas at very low pressure, said means having a generallycylindrical shape and enveloping a collector electrode which closelyconforms to the shape of the cylindrical portion of said means, a gridelectrode consisting of a conductive strand crimped in a zigzagconfiguration to define a generally rec-v tangular shape, a filamentelectrode consisting of a conductive strand crimped to form an invertedV, said grid electrode and filament electrode being juxtaposed in andenveloped by said cylindrical collector electrode.

STANLEY BASHKIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,372,798 Buckley 1 Mar. 29, 19211,723,869

Langmuir Aug. 6, 1929

